(Chapra, L19) Dave Reckhow (UMass) CEE 577 #12 1 The impacts of - - PowerPoint PPT Presentation

Lecture #12 BOD and Oxygen Saturation

(Chapra, L19)

Dave Reckhow (UMass) CEE 577 #12 1

Updated: 23 October 2017

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The impacts of low O2 in water

 Channel catfish mortality due to low dissolved oxygen.

 From: Auburn University, school of fisheries

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Dissolved Oxygen (D.O.)

 Oxygen is a rather insoluble gas, and as a

result its is often the limiting constituent in the purification of wastes and natural waters. Its solubility ranges from 14.6 mg/l at 0oC to about 7 mg/l at 35oC. In addition to temperature, its solubility varies with barometric pressure and salinity. The saturation concentration of oxygen in distilled water may be calculated from the following empirical expression:

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DO saturation formula

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( )

( )(

)

C C P P wv P P P

s sl wv

= −             − − −               1 1 1 1 θ θ where: Pvw = water vapor partial pressure (atm) = 11.8571 - (3840.70/Tk) + (216,961/Tk

2)

P = total atmospheric (barometric) pressure (atm), which may be read directly or calculated from a remote reading at the same time from: = Po - (0.02667)∆H/760 ∆H = Difference in elevation from the location of interest (at P) to the reference location (at Po) in feet.

DO (cont.)

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Po = Simultaneous barometric pressure at a nearby reference location θ = pressure/temperature interactive term = 0.000975 - (1.426x10-5T) + (6.436x10-8T2) T = Temperature in degrees centigrade Cs1 = Saturation concentration of oxygen in distilled water at 1 atmosphere total pressure. ln(Cs1) = -139.34411 + (1.575701x105/Tk) - (6.642308x107/Tk

2) + (1.243800x1010/Tk 3) -

(8.621949x1011/Tk

4).

Tk = Temperature in degrees Kelvin (Tk = T + 273.15)

DO temperature profile

Dave Reckhow (UMass) CEE 577 #12 6 http://www.fondriest.com/environmental- measurements/parameters/water- quality/dissolved-oxygen/

DO Temperature Profile

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Oxygen and aquatic systems

Dave Reckhow (UMass) CEE 577 #12 8 http://www.fondriest.com/environmental- measurements/parameters/water- quality/dissolved-oxygen/

DO (cont.)

 Minimum concentration is required for the survival

• f higher aquatic life

 larval stages of certain cold-water fishes are quite sensitive

 Significant discharges of organic wastes may

depress the D.O. concentrations in receiving waters

 microbially-mediated oxidation

 each state has established ambient dissolved oxygen standards

 Another use of D.O. is the assessment of

• xidation state in groundwaters and sediments

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DO (cont.)

 also a very important parameter in biological

treatment processes

 indicate when aerobic and anaerobic organisms will predominate

 used to assess the adequacy of oxygen transfer systems

 indicate the suitability for the growth of such sensitive organisms

such as the nitrifying bacteria.

 used in the assessment of the strength of a

wastewater through either the Biochemical Oxygen Demand (BOD) or respirometric studies.

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Dissolved Oxygen

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Solutions

• reduction of BOD by biological WW treatment
• nutrient control

Ambient Water Quality Criteria

• established by EPA in "Gold Book"
• dependent on type of fish, averaging period

Ambient Water Quality Standards [enforceable]

• established by states, and other local agencies
• dependent on use classification

Oxygen Demand

 It is a measure of the amount of “reduced”

• rganic and inorganic matter in a water

 Relates to oxygen consumption in a river or lake

as a result of a pollution discharge

 Measured in several ways

 BOD - Biochemical Oxygen Demand  COD - Chemical Oxygen Demand  ThOD - Theoretical Oxygen Demand

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BOD: A Bioassay

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Briefly, the BOD test employs a bacterial seed to catalyze the

• xidation of 300 mL of full-strength or

diluted wastewater. The strength of the un-diluted wastewater is then determined from the dilution factor and the difference between the initial D.O. and the final D.O. BOD Bottle

BOD DO DO

t i f

≡ −

Chapra’s Glucose example

2 4 6 8 10 12 5 10 15 20 25 Time (days) Oxygen (mg/L) Glucose Oxygen

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C6H12O6 + 6O2 = 6CO2 + 6H2O

Lt ∆ D.O.

BOD with dilution

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t i f s b

BOD = DO - DO V V      

Where BODt = biochemical oxygen demand at t days, [mg/L] DOi = initial dissolved oxygen in the sample bottle, [mg/L] DOf = final dissolved oxygen in the sample bottle, [mg/L] Vb = sample bottle volume, usually 300 or 250 mL, [mL] Vs = sample volume, [mL]

When BOD>8mg/L

BOD - loss of biodegradable organic matter (oxygen demand)

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Lo Lt L or BOD remaining Time Lo-Lt = BODt BOD Bottle BOD Bottle BOD Bottle BOD Bottle BOD Bottle

The BOD bottle curve

 L=oxidizable carbonaceous material remaining to be oxidized

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5 10 15 20 25 30 35 2 4 6 8 Time (days) BOD or Y (mg/L)

BOD y L L

t t

• t

≡ = −

CBOD

NBOD

Lt Lo

 To next lecture

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